Methods for fabricating optical microstructures using a cylindrical platform and a rastered radiation beam

ABSTRACT

Optical microstructures, such as microlenses, are fabricated by rotating a cylindrical platform that includes a radiation sensitive layer thereon, about its axis, while simultaneously axially rastering a laser beam across at least a portion of the radiation sensitive layer. The cylindrical platform is also simultaneously translated axially while it is being rotated. The amplitude of the laser beam is continuously varied while rastering. The optical microstructures that are imaged in the radiation sensitive layer can be developed to provide a master for replicating a microlenses.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/661,916,filed Sep. 11, 2003, now U.S. Pat. No. 7,190,387 entitled Systems forFabricating Optical Microstructures Using A Cylindrical Platform and aRastered Radiation Beam, and is related to application Ser. No.10/661,917, filed Sep. 11, 2003, entitled Systems and Methods ForMastering Microstructures Through a Substrate Using Negative Photoresistand Microstructure Masters So Produced to the present inventors, andapplication Ser. No. 10/661,974, filed Sep. 11, 2003, entitled Systemsand Methods For Fabricating Microstructures By Imaging A RadiationSensitive Layer Sandwiched Between Outer Layers, and MicrostructuresFabricated Thereby to the present inventors, all of which are assignedto the assignee of the present application, the disclosures of all ofwhich are hereby incorporated herein by reference in their entirety asif set forth fully herein.

FIELD OF THE INVENTION

This invention relates to microfabricating methods and systems, and moreparticularly to systems and methods for fabricating microstructures andmicrostructures fabricated thereby.

BACKGROUND OF THE INVENTION

Optical microstructures are widely used in consumer and commercialproducts. As is well known to those having skill in the art, opticalmicrostructures may include microlenses, optical gratings,microreflectors and/or other optically absorbing, transmissive and/orreflective strictures, the individual sizes of which are on the order ofmicrons, for example on the order of about 5 μm to about 1000 μm insize.

The fabrication of large arrays of optical microstructures is currentlybeing investigated. As used herein, a large array of opticalmicrostructures contains at least about one million opticalmicrostructures and/or covers an area of at least about one foot square.For example, large arrays of microlenses may be used in computerdisplays (monitors) and/or projection televisions. It will be understoodthat an array can have uniform and/or nonuniform spacing of identicaland/or nonidentical microstructures.

Unfortunately, however, severe scaling barriers may be encountered inattempting to fabricate large arrays of optical microstructures. Thesescaling barriers may make it difficult to efficiently produce largearrays of optical microstructures with acceptable manufacturing yields.

Several barriers may be encountered in attempting to scale opticalmicrostructures to large arrays. First, the time to master a large arraymay be prohibitive. In particular, it is well known that opticalmicrostructures may be initially imaged in a “master”, which may then bereplicated in one or more second generation stampers to eventuallyproduce large quantities of end products. Unfortunately, it may bedifficult to produce a master for a large array of opticalmicrostructures within a reasonable time. For example, calculations mayshow that it may take years to create a single master for large screenrear projection television. These mastering times may be prohibitive forviable products.

It also may be difficult to image certain optical microstructures thatmay be desired for many applications. For example, computer displays orprojection televisions may employ large arrays of microlenses, whereineach microlens comprises a hemispherical section, which can include asub-hemisphere (subtends less than 180°), hemisphere (subtends about180°) or super-hemisphere (subtends more than 180°). However, it may bedifficult to master a large array of hemispherical sections usingconventional photolithographic techniques. Finally, it may be difficultto efficiently replicate masters containing large arrays of opticalmicrostructures to produce stampers, so as to enable high volumeproduction of optical microstructure end products for display,television and/or other applications.

SUMMARY OF THE INVENTION

Some embodiments of the present invention fabricate opticalmicrostructures, such as microlenses, by rotating a cylindrical platformthat includes a radiation sensitive layer thereon, about an axisthereof, while simultaneously axially rastering a radiation beam acrossat least a portion of the radiation sensitive layer, to image theoptical microstructures in the radiation sensitive layer. The opticalmicrostructures that are imaged in the radiation sensitive layer can bedeveloped to provide a master for optical microstructures.

In some embodiments, the cylindrical platform is also simultaneouslytranslated axially while it is being rotated. The cylindrical platformmay be continuously translated axially to image the opticalmicrostructures in a spiral pattern in the radiation sensitive layer,and/or stepwise translated axially to image the optical microstructuresin a band pattern in the radiation sensitive layer. When stepwisetranslating, some embodiments can stepwise translate at a predeterminedrotation angle, to image the optical microstructures in an aligned bandpattern in the radiation sensitive layer. Other embodiments can stepwisetranslate the cylindrical platform axially at staggered rotation angles,which may be uniform and/or non-uniform staggered rotation angles, toimage the optical microstructures in a staggered band pattern in theradiation sensitive layer. Combinations of aligned and staggeredrotation angles also may be provided.

In some embodiments of the present invention, while rastering theradiation beam across at least a portion of the radiation sensitivelayer, the amplitude of the radiation beam is varied to image theoptical microstructures in the radiation sensitive layer. In someembodiments, the amplitude of the radiation beam is continuously varied,so as to image optical microstructures such as hemispherical sectionlenses, in the radiation sensitive layer. In other embodiments,rastering may be performed at sufficient speed, relative to rotating thecylindrical platform, such that the radiation beam images a singleoptical microstructure over multiple scans of the radiation beam.

In some embodiments, the focal length of the radiation beam may bevaried during rastering, to at least partially compensate for radialvariations in the cylindrical platform and/or thickness variations inthe radiation sensitive layer. In other embodiments, the focal lengthmay be varied to image portions of the optical microstructures atvarying depths in the radiation sensitive layer. In some embodiments,imaging of the radiation beam takes place along first and secondopposite axial directions, whereas in other embodiments, imaging takesplace along a first axial direction and the radiation beam may beblanked during a return along the second axial direction.

In some embodiments, the radiation beam is a coherent radiation beamsuch as a laser or electron beam. Axial rastering may be provided bygenerating a continuous wave laser beam, modulating the laser beam tovary an amplitude thereof, and oscillating the laser beam to raster thelaser beam across at least a portion of the radiation sensitive layer.

In some embodiments of the present invention, the cylindrical platformis at least about one foot in circumference and/or at least about onefoot in axial length, so as to fabricate large numbers of opticalmicrostructures thereon. Rotating may be performed at angular velocitiesof at least about 1 revolution/minute, and/or axial rastering may beperformed at a frequency of at least about 1 kHz. Moreover, in someembodiments, rotating and simultaneously axially rastering may beperformed continuously for at least about 1 hour, to fabricate at leastabout one million microstructures.

In some embodiments, the cylindrical platform also includes a substrateon the radiation sensitive layer, which is transparent to the radiationbeam. In these embodiments, simultaneously axially rastering isperformed by simultaneously axially rastering a radiation beam throughthe substrate that is transparent thereto across at least a portion ofthe radiation sensitive layer, to image the microstructures in theradiation sensitive layer. In some embodiments, the radiation sensitivelayer is a negative photoresist layer, such that portions of thenegative photoresist layer that are exposed to the radiation beam remainafter development. In some embodiments, the substrate is a flexiblesubstrate.

In yet other embodiments, the radiation sensitive layer is sandwichedbetween a pair of outer layers on the cylindrical platform and at leastone of the outer layers is removed after imaging. More specifically, insome embodiments, the pair of outer layers includes a first outer layeradjacent the cylindrical platform and a second outer layer remote fromthe cylindrical platform that is transparent to the radiation beam. Inthese embodiments, the radiation beam is axially rastered through thesecond outer layer across at least a portion of the radiation sensitivelayer. In some embodiments, after imaging, the first outer layer isseparated from the cylindrical platform, and the first outer layer isthen separated from the radiation sensitive layer.

Embodiments of the invention have been described above primarily withrespect to methods of fabricating optical microstructures. However, itwill be understood by those having skill in the art that otherembodiments of the invention can provide analogous systems forfabricating optical microstructures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 are perspective views of systems and methods of fabricatingmicrostructures according to various embodiments of the presentinvention.

FIGS. 5A-5C and 6A-6C illustrate rastering of a radiation beam across atleast a portion of a radiation sensitive layer according to variousembodiments of the present invention.

FIG. 7 is a block diagram of systems and methods for fabricating opticalmicrostructures according to other embodiments of the present invention.

FIG. 8 is a cross-sectional view of systems and methods for fabricatingoptical microstructures according to yet other embodiments of thepresent invention.

FIGS. 9-11 are perspective views of systems and methods for fabricatingoptical microstructures according to still other embodiments of thepresent invention.

FIG. 12 is a cross-sectional view of systems and methods for fabricatingoptical microstructures according to other embodiments of the presentinvention.

FIG. 13A is a cross-sectional view of systems and methods forfabricating optical microstructures according to still other embodimentsof the present invention.

FIG. 13B is a cross-sectional view of an imaged negative photoresistlayer after development according to embodiments of the presentinvention.

FIG. 14 is a flow diagram illustrating replication of a master intostampers and end products according to various embodiments of thepresent invention.

FIGS. 15 and 16 are cross-sectional views of optical microstructuresthat are fabricated using conventional front-side imaging with positivephotoresist.

FIGS. 17-19 are cross-sectional views of systems and methods forfabricating optical microstructures according to other embodiments ofthe present invention.

FIG. 20 is a cross-sectional view of optical microstructures accordingto some embodiments of the present invention.

FIGS. 21 and 22 are flowcharts illustrating operations that may beperformed to fabricate optical microstructures according to variousembodiments of the present invention.

FIG. 23 is a schematic diagram of systems and methods that may be usedto fabricate optical microstructure master blanks according to someembodiments of the present invention.

FIG. 24 is a cross-sectional view of an optical microstructure masterblank according to some embodiments of the present invention.

FIGS. 25A-25E, 26A-26B and 27 are cross-sectional views of systems andmethods of fabricating optical microstructures according to variousembodiments of the present invention.

FIG. 28 is a schematic view of systems and methods for mass productionof masters and stampers for optical microstructures according to someembodiments of the present invention.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, the size and relative sizes of layers and regions may beexaggerated for clarity. Like numbers refer to like elements throughout.

It will be understood that when an element such as a layer, region orsubstrate is referred to as being “on” another element, it can bedirectly on the other element or intervening elements may also bepresent. Furthermore, relative terms such as “top” or “outer” may beused herein to describe a relationship of one layer or region to anotherlayer or region relative to a base structure as illustrated in thefigures. It will be understood that these relative terms are intended toencompass different orientations of the device in addition to theorientation depicted in the figures. Finally, the term “directly” meansthat there are no intervening elements.

Embodiments of the present invention will be described herein relativeto the fabrication of optical microstructures, which may includemicrolenses, optical gratings, microreflectors and/or otheroptically-absorbing transmissive and/or reflective structures, theindividual sizes of which are on the order of microns, for example onthe order of about 5 μm to about 1000 μm, in size. However, it will beunderstood that other embodiments of the present invention may be usedto fabricate mechanical microstructures such as pneumatic, hydraulicand/or microelectromechanical system (MEMS) microstructures, which maybe used for micro-fluidics, micro-pneumatics and/or micromechanicalsystems, the individual sizes of which are on the order of microns, forexample on the order of about 5 μm to about 1000 μm, in size.

FIG. 1 is a perspective view illustrating systems and methods offabricating optical microstructures according to some embodiments of thepresent invention. As shown in FIG. 1, a cylindrical platform or drum101 that includes a radiation sensitive layer 110 thereon, is rotatedabout an axis 102 thereof, for example in a direction shown by the arrow104. As used herein, the term “radiation sensitive” encompasses anyphoto-imageable material, including, but not limited to, photoresist. Asalso shown in FIG. 1, simultaneously, a radiation beam such as a laserbeam 120, generated by a laser 122, is axially rastered or scanned inopposite axial directions shown by the arrows 124, across at least aportion of the radiation sensitive layer 110, to image opticalmicrostructures 132 in the radiation sensitive layer 110. The image soformed may also be referred to as a latent image. It will be understoodthat, although embodiments of the invention are generally describedherein with respect to laser beams and laser sensitive photoresists,other coherent or incoherent radiation beams, such as electron beams,may be used, along with compatible radiation sensitive layers.

It will also be understood by those having skill in the art that theradiation sensitive layer 110 may be directly on the cylindricalplatform 100, as shown in FIG. 1, or one or more intervening layers maybe provided between the radiation sensitive layer 110 and thecylindrical platform 100, as will be described in detail below.Moreover, one or more layers may be provided on the radiation sensitivelayer 110, remote from the cylindrical platform 100, as will bedescribed in detail below. Other embodiments of the radiation sensitivelayer 110 also will be described below. Moreover, the cylindricalplatform 100 may be rotated about axis 102 at a constant angularvelocity and/or at variable angular velocity.

Still referring to FIG. 1, in some embodiments, the laser 122 is aContinuous Wave (CW) laser that emits radiation at a frequency orfrequency band to which the radiation sensitive layer 110 is sensitive.In some embodiments, the laser beam 120 may be rastered axially over theentire axial length of the cylindrical platform. However, in otherembodiments, as will be described in more detail below, the laser beam124 may be rastered over relatively small portions of the cylindricalplatform 100.

Finally, it will be understood that, although only a small number ofoptical microstructures 132 are shown for the sake of illustration,conventionally large numbers of optical microstructures 132 arefabricated to provide, in some embodiments, a large array of opticalmicrostructures. Although optical microstructures 132 are shown in FIG.1 as being microlenses in the shape of a hemispherical section, in otherembodiments other microstructures, such as optical grating structures,may be formed as a plurality of uniformly and/or non-uniformly spaced,identical and/or non-identical optical microstructures 132. Combinationsof different types of optical microstructures, with uniform and/ornonuniform sizes and/or spacings, also may be fabricated.

FIGS. 2-4 illustrate other embodiments of the present invention whereinthe cylindrical platform 100 and/or the laser beam 120 are translatedaxially relative to one another, simultaneous with the platform rotationand beam rastering, to image the optical microstructures across at leasta substantial portion of the length of the cylindrical platform 100. Insome embodiments, the axial translation can allow opticalmicrostructures to be formed across substantially the entire axiallength of the cylindrical platform 100. In some embodiments, thecylindrical platform 100 may be maintained at a fixed axial position andthe laser 122 and/or the laser beam 120 may be translated along theaxial direction. In other embodiments, the laser 122 and/or laser beam120 may be maintained in a fixed axial location and the cylindricalplatform 100 may be translated axially. In still other embodiments, boththe laser 122 and/or laser beam 122, and the cylindrical platform 100,may be translated relative to one another axially. For example, thelaser 122 may be fixed at one end of the cylindrical platform 100 andlaser optics such as a mirror may be configured to translate the laserbeam 122 relative to the cylindrical platform, for example by movingaxially and/or rotating.

FIGS. 2-4 illustrate embodiments of the present invention wherein thecylindrical platform 100 is translated axially relative to a fixed laser122. More specifically, referring to FIG. 2, the cylindrical platform100 is translated axially along an axial translation direction shown byarrow 224, by moving a support 210 relative to a base 220 using rollers222 and/or other conventional mechanisms. As shown in FIG. 2, continuoustranslation of the cylindrical platform 110 along the translationdirection 224 is provided, to thereby image the optical microstructures132 in a continuous spiral pattern 230 in the radiation sensitive layer110.

FIG. 3 illustrates other embodiments of the present invention wherein astepwise translation of the cylindrical platform 100 relative to thelaser beam 120, along a translation direction 324, is provided, tothereby image the optical microstructures 132 in discrete bands 330 inthe radiation sensitive layer. In embodiments of FIG. 3, continuousrotation of the cylindrical platform 100 in the rotation direction ofarrow 104 may be provided and stepwise translation of the cylindricalplatform may be provided along a translation direction 324 after anindividual band 330 has been imaged. It will be understood that thecylindrical platform 100 may continue to rotate through less than one,one, or more than one complete revolutions during the stepwisetranslation of the cylindrical platform 100.

In FIG. 3, imaging of each band 330 begins and ends at the samepredetermined rotation angle of the cylindrical platform 100, to therebyprovide a pattern of aligned bands 330 in the radiation sensitive layer110. A guardband may be provided in a band, to separate the beginningand end of the band from one another. Alternatively, the beginning andend of a band may abut against one another.

In contrast, in FIG. 4, the cylindrical platform 100 is stepwisetranslated axially along the translation direction 324 at staggeredrotation angles of the cylindrical platform 100, to thereby image theoptical microstructures 132 in a staggered band pattern 430. In someembodiments, the beginning and/or ends of a band may be uniformlystaggered relative to one another, as shown by the band beginnings/ends432. In other embodiments, non-uniform staggering of bandbeginnings/ends, as shown at 434, may be provided. Combinations ofaligned (FIG. 3) and staggered (FIG. 4) band patterns also may beprovided. It also will be understood that combinations of the imagingsystems and methods of FIGS. 1-4 may be provided in a single radiationsensitive layer 110. In some embodiments, the spiral/band structures ofFIGS. 2-4 may not be detected after all the optical microstructures areimaged and developed so that uniformly spaced optical structures areproduced. However, in other embodiments, at least some aspects of thespiral/band structures may be detected after development.

FIGS. 5A-5C and 6A-6C illustrate the rastering of a radiation beam, suchas a laser beam 120, across at least a portion of a radiation sensitivelayer, such as a radiation sensitive layer 110 of FIG. 1, to imageoptical microstructures, such as the optical microstructures 132 ofFIGS. 1-4, in the radiation sensitive layer, according to variousembodiments of the present invention. For ease of illustration, only aportion of the radiation sensitive layer 110 and the microstructures 132are shown.

FIG. 5A is a top view of a portion of the radiation sensitive layer 110and FIG. 5B is a cross-sectional view of the radiation sensitive layer110 taken through line 5B-5B′ of FIG. 5A. As shown in FIGS. 5A and 5B,the radiation beam, such as the laser beam 120 of FIGS. 1-4, is axiallyrastered across at least a portion of the radiation sensitive layer 110,to image the optical microstructures 132 in the radiation sensitivelayer, by axially rastering the laser beam 120 across at least a portionof the radiation sensitive layer 110, while varying the amplitude of thelaser beam. More specifically, as shown in FIGS. 5A-5C, axial rasteringtakes place by axially rastering the laser beam 120 across at least aportion of the radiation sensitive layer 110 while varying the amplitudeof the laser beam, to thereby image the optical microstructures 132 inthe radiation sensitive layer 110. In particular, as shown in FIG. 5A,in some embodiments, the rastering may provide three scans 510, 512, 514across the radiation sensitive layer 110 in the axial direction 124. Thescans are spaced apart from one another due to the rotation of thecylindrical platform 100. In FIG. 5A, the laser beam is rastered along afirst axial direction, shown as to the right in FIG. 5A, to image theoptical microstructures and then blanked, as shown by dashed lines 520,522 and 524 in a second axial direction that is opposite the first axialdirection, shown as to the left in FIG. 5A. During the axial scans 510,512, 514, the amplitude of the laser beam may be varied as shown in FIG.5C, to produce the optical microstructures 132.

Thus, as shown in FIGS. 5A-5C, the amplitude of the laser beam 120 iscontinuously varied to image the optical microstructures 132 in theradiation sensitive layer 110. Moreover, the axial rastering isperformed at sufficient speed, relative to the rotating of thecylindrical platform 100, such that the laser beam 120 images an opticalmicrostructure 132 over a plurality of scans of the laser beam, shown asthree scans 510, 512, 514 in FIGS. 5A-5C. It will be understood that, insome embodiments, an optical microstructure may be imaged in a singlescan and, in other embodiments, two scans or more than three scans maybe used. Moreover, in some embodiments, a plurality of lasers may beused to perform more than one scan simultaneously.

It also will be understood that the amplitude of the laser beam 120 maynot be a linear function of the shape of the optical microstructure thatis being imaged, due to nonlinear absorption/development characteristicsof the radiation sensitive layer 110 and/or other well-known nonlineareffects. In particular, the prediction of the shape that will resultfrom the imaging may involve a detailed understanding not only of thebeam profile and intensity, and the way in which they vary in space andtime, but also the manner in which the radiation sensitive layerresponds to the radiation energy deposited in it (“exposure curves”). Inaddition to the parameters involved in the exposure, the response of theradiation sensitive layer can also be affected by various post-exposuredevelopment parameters. The desired amplitude of the laser beam 120during a scan may be determined empirically by trial and error, toarrive at a desired amplitude that produces a desired image of anoptical microstructure, by using simulators, by using a mathematicalconvolution function that defines the relationship between laser doseand a developed image in a radiation sensitive layer and/or by usingother conventional techniques that need not be described in detailherein.

FIGS. 6A-6C illustrate other embodiments of the invention wherein theradiation sensitive layer 110 is imaged during forward and returnscanning of the laser beam rather than blanking the laser beam 120during its return. Higher density and/or higher speed may thereby beobtained at the potential expense of greater complexity. Thus, as shownin FIGS. 6A-6C, imaging is performed in a first (forward) axialdirection, shown as to the right in FIG. 6A by scan lines 610, 612 and614, and in a second direction that is opposite the first direction,shown as to the left in FIGS. 6A-6C, during return scans 620 and 622. Aswas the case with respect to FIG. 5, fewer or larger numbers of scansmay be provided. It also will be understood that embodiments of FIGS. 5and/or 6 may be combined with any of the embodiments of FIGS. 1-4.

FIG. 7 is a block diagram of other systems and methods for fabricatingoptical microstructures according to other embodiments of the presentinvention. As shown in FIG. 7, a continuous wave laser beam 120 isgenerated by a continuous wave laser 710, and power controlstabilization may be provided by a power control stabilizer 712. Inother embodiments, a “quasi-continuous wave” laser beam may be provided,using, for example, a switchable semiconductor laser. A modulator 714,which in some embodiments may be an acoustooptical (AO) modulator 714,is used to vary the amplitude of and raster the laser beam 120. In someembodiments, separate modulators may be used to modulate the amplitudeof the laser beam 120 and to raster the position of the laser beam 120.The modulator 714 is capable of imparting angular deflection to thebeam, to provide a limited range of motion, without having to move theplatform 100 on which the radiation sensitive layer 110 is placed.Moreover, other conventional techniques for changing the amplitudeand/or position of the laser beam 120 also may employed. For example,the amplitude of the laser beam may be changed at the laser 710 itself,and the position may be rastered using a conventional scanner thatemploys rotating and/or oscillating mirrors.

Continuing with the description of FIG. 7, a mirror, prism and/or otheroptical element(s) 716 may be used to change the direction of the laserbeam 120 if desired. Beam shaping optics 718 may be used to control theshaping of the laser beam 120, to form an ellipsoidal (such as circular)and/or polygonal (such as square) beam with an intensity profilethereacross which may be constant, Gaussian and/or follow otherconventional profiles. An auto-focus system 722 also may be provided tocontrol the focal point of the laser beam 120 relative to thecylindrical platform 100. The design and operation of Blocks 710-722 arewell known to those having skill in the art and need not be described indetail herein. These blocks may be referred to collectively as anoptical train, or as a radiation beam system. Moreover, it will beunderstood that some of the Blocks 712-722 need not be used in opticaltrains or radiation beam systems according to other embodiments of thepresent invention. Accordingly, embodiments of FIG. 7 can generate acontinuous wave laser beam 120 and modulate the laser beam to vary anamplitude thereof, while simultaneously oscillating the laser beam toraster the laser beam across at least a portion of the radiationsensitive layer 110.

In particular, it may be difficult to fabricate microstructures withuniform and/or varying profiles and/or heights with high accuracy. Someembodiments of the present invention can use continuously varyingintensity radiation beam, such as a laser beam 120, to form opticalmicrostructures. This can allow creation of arbitrary three-dimensionalprofiles of optical elements in real time with high accuracy. In orderto produce features at a high enough rate to permit the mastering oflarge numbers of optical microstructures using multiple exposures peroptical microstructure, the laser beam 120 may be modulated in intensityand spatially at a rate of at least about 1 kHz and, in someembodiments, at MHz rates. AO modulation can provide this capacity,since the beam can be rastered and amplitude modulated at thesefrequencies. The focal plane or other aspects of the beam profile alsomay be changed rapidly, to vary the depth in the radiation sensitivelayer 110 at which a maximum amount of radiation energy is deposited.

Still continuing with the description of FIG. 7, a control system and/ormethod, also referred to herein as a controller, also may be provided.The controller 730 may include dedicated hardware and/or one or moreenterprise, application, personal, pervasive or embedded computersystems that may be interconnected via a network, to execute one or morecomputer programs. The controller 730 may be centralized and/ordistributed. The controller 730 may be used to control some or all ofblocks 710-722 using conventional control techniques. In addition, thecontroller 730 may be designed to control the angular rotation θ of thecylindrical platform 100, the translation X of the cylindrical platform100, and the amplitude and position of the laser beam 120 relative totime, to image optical microstructures according to any of theembodiments that are described herein, or combinations thereof. Thedesign of a controller is well known to those having skill in thecontrol art, and need not be described further herein.

In some embodiments, the controller 730 is capable of synchronizing thebeam exposure and placement as provided by Blocks 710-722, with thedesired physical location on the radiation sensitive layer 110 where theexposure is to take place. In some embodiments, systems/methods of FIG.7 may be in operation for periods of up to about 24 hours or more at atime, so that the controller 730 should be capable of maintainingparameters within their desired tolerances over this period of time.

Moreover, in some embodiments of the present invention, the controller730 can control an auto-focus system 722, to perform additionalfunctions. In particular, in some embodiments, the focal length of thelaser beam 120 may be varied simultaneous with the rotation of thecylindrical platform 100 and the axial rastering the laser beam 120, toat least partially compensate for radial variation in the cylindricalplatform 100 and/or thickness variation in the radiation sensitive layer110. In other embodiments, the focal length of the laser beam 120 alsomay be varied to image portions of the optical microstructures atvarying depths in the radiation sensitive layer 110. In still otherembodiments, the focal length of the laser beam 120 is varied to varythe exposure of the radiation sensitive layer 110, to provide thedesired optical microstructure. Combinations and subcombinations ofthese focal length control mechanisms may be provided, alone or incombination with amplitude control of the laser beam 120.

In some embodiments, the optical microstructures 132 that is imaged inthe radiation sensitive layer 110 of FIGS. 1-7 is developed at adeveloping station, as will be described in detail below. The developedradiation sensitive layer can provide a master for opticalmicrostructure end products, which may be used, for example, in computerdisplays and/or televisions.

Additional discussion of embodiments of the present invention that wereillustrated in FIGS. 1-7 now will be provided. In particular, as wasdescribed above, conventional approaches for mastering opticalmicrostructures may encounter severe scaling barriers when applied to atleast about one million elements and/or covering at least about one footsquare in area. In these structures, it may be difficult to image amaster in a reasonable time. In sharp contrast, some embodiments of thepresent invention can perform on the order of one million separateexposures per second, with sufficient resolution and accuracy to produceon the order of 10,000 optical microstructures per second, so that amaster for a large rear screen projection television can be fabricatedin hours, rather than years using conventional technologies.

Some embodiments of the present invention can place a small laser beam,for example of diameter of about 5 μm, of sufficient intensity to exposea radiation sensitive layer, and modulate this beam in intensity andlocation at, for example, MHz speeds. A cylindrical platform on whichthe radiation sensitive layer can be placed or mounted, can be movedaccurately and quickly by computer control. A control systemsynchronizes the placement of the modulated beam on the platform, toexpose the proper portion of the radiation sensitive layer with thecorrect amount of radiation.

Dimensions and speeds according to some embodiments of the presentinvention will now be provided, to provide an appreciation of the scalein which some embodiments of the present invention may operate. However,these dimensions and speeds shall be regarded as examples, and shall notbe regarded as limiting. In particular, in some embodiments of thepresent invention, the cylindrical platform 100 may be about three feetin length and about five feet in circumference. The radiation sensitivelayer 110 may be between about 10 μm and about 150 μm thick. A band ofthe rastered laser beam 124 may be between about 1 μm and about 1000 μmin axial length. A hemispherical section lens that is about 75 μm indiameter may be fabricated using 10 scans per lens, wherein return scansare blanked. The cylindrical platform 100 may rotate at an angularvelocity of about 60 revolutions/minute and the rastering may beperformed at a frequency of about 500,000 scan/sec. Given theseparameters, it may take about 2 hours to fabricate about 200 millionmicrolenses.

FIG. 8 is a cross-sectional view of systems and methods for fabricatingoptical microstructures according to other embodiments of the presentinvention. As shown in FIG. 8, a radiation beam such as a laser beam 820from a laser 822, which may correspond to the laser 110 and/or 710 ofFIGS. 1-7, is impinged through a substrate 800 that is transparentthereto into a radiation sensitive layer 810 thereon, which maycorrespond to the radiation sensitive layer 110 of FIGS. 1-7, to imageoptical microstructures 832, which may correspond to opticalmicrostructures 132 of FIGS. 1-7, in the radiation sensitive layer 810.As was already described, the radiation beam may be coherent and/orincoherent. Moreover, as used herein, a “transparent” substrate allowsat least some of the incident radiation to pass therethrough. Imaging ofa radiation beam through a substrate that is transparent thereto into aradiation sensitive layer 810 on the substrate may be referred to hereinas “back-side” imaging or “substrate incident” imaging. It will beunderstood by those having skill in the art that, in FIG. 8, althoughthe substrate 800 is shown above the radiation sensitive layer 810,other orientations of the substrate 800, radiation sensitive layer 810,laser beam 820 and laser 822 may be used to provide back-side imaging,according to various embodiments of the present invention.

Moreover, in providing back-side imaging of radiation sensitive layers810 to fabricate optical microstructures 832 according to someembodiments of the present invention, many systems and methods may beused to move the laser beam 820 and the substrate 800 relative to oneanother. Some of these systems and methods are illustrated in FIGS.9-11.

In particular, referring to FIG. 9, a cylindrical platform 900, whichmay correspond to the platform 100 of FIGS. 1-7, may be used accordingto any of the embodiments that were described above in connection withFIGS. 1-7. Thus, as shown in FIG. 9, a laser beam 820 is impingedthrough a cylindrical substrate 800 into a cylindrical radiationsensitive layer 810 that is on a cylindrical platform 900. The substrate800 may be flexible. In yet other embodiments, the structure of FIG. 9may be used independent of any of the embodiments of FIGS. 1-7.Moreover, in still other embodiments, the laser beam 820 may be producedand/or directed inside the cylindrical platform 900, and the cylindricalplatform 900 may constitute a transparent substrate.

FIG. 10 illustrates other embodiments wherein a laser beam 820 isimpinged through a polygonal substrate 800′ into a polygonal-shapedradiation sensitive layer 810′ that is on a polygonal platform 1000. Insome embodiments, the substrate 800′ is rectangular or square, theradiation sensitive layer 810′ is rectangular or square, and thepolygonal platform 1000 is a rectangular or square high precision X-Ytable that can be translated continuously and/or in a stepwise manneralong orthogonal X and/or Y directions, as shown in FIG. 10.

Finally, FIG. 11 illustrates other embodiments wherein a laser beam 820is impinged through an ellipsoidal substrate 800″ into an ellipsoidalradiation sensitive layer 810″ on an ellipsoidal platform 1100. In someembodiments, the ellipsoidal substrate 800″ is a circular substrate800″, the ellipsoidal radiation sensitive layer 810″ is a circularradiation sensitive layer, and the ellipsoidal platform 1100 is acircular platform that is mounted on a spindle 1104 for rotation, asshown by arrow 1102.

In any of the embodiments of FIGS. 9-11, an optical train or systemcorresponding, for example, to elements 710, 712, 714, 716, 718 and/or722 of FIG. 7 may be provided, along with a controller such ascontroller 730 of FIG. 7. Similarly, in any of the embodiments of FIGS.9-11, the laser beam may be maintained stationary and/or may berastered, and relative translation between the radiation sensitive layerand the laser beam may be provided by translation of the laser 822, thelaser beam 820 and/or the platform 100, 1000 or 1100, as was alreadydescribed in connection with FIGS. 1-7.

FIG. 12 is a cross-sectional view of other embodiments of the presentinvention. In these embodiments, a negative photoresist layer 1210 isused as a radiation sensitive layer, with or without a substrate 1200,and a radiation beam such as a laser beam 820 is impinged into thenegative photoresist layer. Embodiments of FIG. 12 may be used incombination with any of the embodiments described above or which will bedescribed below.

As is well known to those having skill in the art, photoresist isavailable in two tones: positive and negative. Positive photoresist isdesigned so that the areas of photoresist that are exposed to radiationare removed in the development process. Negative photoresist is designedso that the areas of photoresist that are exposed to radiation remainafter development and the unexposed portions are removed. Both typeshave been used in conventional integrated circuit fabrication, althoughpositive photoresist now may be more commonly used due to its ease ofadaptation to integrated circuit fabrication. Conventionally, negativephotoresist may not be regarded as being applicable for fabricatingoptical microstructures. See, for example, U.S. Published PatentApplication 2002/0034014 entitled Microlens Arrays Having FocusingEfficiency, to Gretton et al., published Mar. 21, 2002.

In particular, in a negative photoresist, only the portion of thephotoresist which is exposed will remain after developing. Thus, in athick film of photoresist, such as may be used to fabricate opticalmicrostructures, only a shallow portion of an outer layer of thephotoresist layer may be exposed. The latent image that is formed byexposure may then be washed away when the unexposed photoresist beneathit is removed during development. Some embodiments of the presentinvention may arise from a realization that negative photoresist mayindeed be used in fabricating optical microstructures. In fact, someembodiments of the invention may arise from a realization that negativephotoresist may provide advantages in fabricating opticalmicrostructures, especially when coupled with back-side imaging. Oneexample of a negative photoresist that can be used is SU-8™, which is anegative photoresist formed of epoxy novolac polymers and marketed byMicroChem Corp.

FIGS. 13A-13B are cross-sectional views of embodiments of the presentinvention that combine back-side imaging of, for example, FIG. 8, alongwith the use of negative photoresist of, for example, FIG. 12. Inparticular, as shown in FIG. 13A, a radiation beam such as a laser beam820 is impinged through a substrate 800 that is transparent thereto intoa negative photoresist layer 1310 on the substrate 800, to image opticalmicrostructures 132 therein. Accordingly, FIG. 13A also illustratesoptical microstructure products, according to some embodiments of theinvention, which include a substrate 800 and an exposed layer ofnegative photoresist 1310 on the substrate 800, which is exposed todefine thereon optical microstructures 132. FIG. 13B illustrates theimaged negative photoresist layer 1310 after development, to formoptical microstructures 132′. Accordingly, FIG. 13B also illustratesoptical microstructure products 1350, according to some embodiments ofthe invention, which may provide an optical microstructure master, andwhich include a substrate 800 and a patterned layer of negativephotoresist on the substrate 800, which is patterned to define opticalmicrostructures 132′ thereon. It will be understood that any of theembodiments of FIGS. 1-11 may be used to fabricate embodiments of FIGS.13A and 13B.

Back-side imaging into a negative photoresist layer according to someembodiments of the present invention may provide many potentialadvantages with respect to the fabrication of an optical microstructuremaster. Some potential advantages now will be described in detail.

In particular, as is well known to those having skill in the art, once amaster is created, a conventional replication process may then beemployed to make multiple copies from the master. Each generation ofreplica generally is a negative of the previous generation. Referring toFIG. 14, a master 1400 may be created using back-side imaging through asubstrate 800 into a layer of negative photoresist thereon, to createoptical microstructures 132′, for example as was described in connectionwith FIGS. 13A and 13B. A large number, for example on the order of upto about 1,000 or more, second generation stampers 1420 may be producedfrom a single master, using conventional techniques. As seen in FIG. 14,the stampers 1420 are negative replicas of the master 1400 withconvexities turned into concavities and vice versa. Then, a largenumber, such as on the order of up to about 1,000 or more, end products1430, such as microlenses for computer displays or televisions, may becreated from each stamper 1420. The end products 1430 are the mirrorimage of the stampers 1420, so that they correspond to a positive imageof the master 1400.

Accordingly, in the example shown in FIG. 14, on the order of up to onemillion or more end products 1430 may be created from a single master1400 using only two generations of replication. In contrast, when usinga positive photoresist, the master may be a negative of the desiredshape, so that the first generation of replicas will be positives. Inorder to produce positive end products, second and third generations ofreplication may need to be provided. Unfortunately, third generationreplicas may not be sufficiently faithful to the original pattern to becommercially viable. In contrast, a negative photoresist can be used tomake a positive copy of the desired shapes in two generations ofreplication, as shown in FIG. 14, so that up to millions or more ofhigh-quality end products 1430 may be produced from a single master1400, according to some embodiments of the invention.

FIGS. 15 and 16 illustrate other potential advantages of back-sideimaging combined with negative photoresist according to some embodimentsof the present invention. In particular, FIG. 15 illustrates an exampleof optical microstructures on a substrate 1500. As shown in FIG. 15, itgenerally may be desirable to form optical microstructures having wallsthat are orthogonal to the substrate 1500, as shown by microstructure1522, or lens or prism microstructures 1524 and 1526, respectively,having bases 1532 adjacent the substrate 1500 and vertices or tips,generally referred to herein as “tops”, 1534, remote from the substrate1500, wherein the bases 1532 are wider than the tops 1534. Moreover, itmay be desirable to form some microstructures, such as microstructure1528, that are short relative to other taller microstructures 1522, 1524and/or 1526.

As shown in FIG. 16, some embodiments of the invention arise from therecognition that it may be difficult to form these shapes usingconventional positive photoresist 1610 and conventionalphotoresist-incident (“front-side”) exposure. In particular, as shown inFIG. 16, when using positive photoresist 1610 and front-side exposure1630 as is conventionally used, for example, in the semiconductorindustry, the radiation acts as a “punch” to image the outer surface ofthe photoresist 1610 opposite the substrate 1600. This relationshiptends to form images 1620 a, 1620 b which are the opposite in shape asthose which may be desired for optical microstructures (FIG. 15).Moreover, as also shown in FIG. 16, relatively shallow images 1620 c mayexist only at the exposed surface of the photoresist layer 1610 and maybe washed away during development. See, for example, Paragraphs 56-67 ofthe above-cited U.S. Published Patent Application 2002/0034014.

In sharp contrast, as was shown, for example, in FIGS. 13A and 13B,back-side imaging combined with negative photoresist, according to someembodiments of the invention, can produce optical microstructures 132′that include bases 1302 adjacent the substrate 800 and tops 1304 thatare narrower than the bases 1302, remote from the substrate 800.Moreover, as shown in FIG. 17, embodiments of the present invention thatimage through the substrate 800 and use negative photoresist 1310 canprovide a photoresist layer 1310 that is thicker than the desiredheights of the optical microstructures 1732, so that the radiation beammay be impinged through the substrate 800 into the negative photoresistlayer 1310 to image buried optical microstructures 1732 in the negativephotoresist layer 1310, adjacent the substrate 800. As long as thenegative photoresist layer 1310 is at least as thick as the thickestoptical microstructure 1732 that is desired to be fabricated, relativelythick and relatively thin microstructures may be fabricated in onenegative photoresist layer, adjacent the substrate 800, and may not bewashed away during the development process.

FIG. 18 illustrates other embodiments of the present invention that mayuse negative photoresist 1310 and imaging by a laser beam 822 throughthe substrate 800. As shown in FIG. 18, when forming a layer of negativephotoresist 1310 over a large substrate 800, the photoresist may havenon-uniform thickness. However, as shown in FIG. 18, as long as theminimum thickness of the negative photoresist layer 1310 is thicker thanthe optical microstructures 1832, then buried optical microstructures1832 may be imaged in the photoresist layer 1310 of variable thickness,adjacent the substrate 800, that may be independent of the variablethickness of the negative photoresist layer 1310.

Other potential advantages of the use of back-side exposure and negativephotoresist, according to some embodiments of the present invention, areshown in FIG. 19. As shown in FIG. 19, the negative photoresist layer1310 may include impurities 1910 thereon. When using conventionalfront-side imaging rather than back-side imaging, these impurities 1910may interfere with the front-side imaging. However, when using back-sideimaging as shown in FIG. 19, the laser beam 822 need not pass through orfocus on, the outer surface 1310 a of the negative photoresist 1310,remote from the substrate 800. Thus, impurities 1910 need not impact theformation of optical microstructures 1832. Accordingly, imaging may takeplace in a non-clean room environment in some embodiments of the presentinvention.

Other potential advantages of the use of negative photoresist mayinclude the fact that its chemistry involves a cross-linking of polymersduring the exposure and development processes, which may provide addedmechanical, chemical and/or thermal stability to the master during thereplication process. In addition, since development may remove the bulkof the negative photoresist layer 1310 from the substrate 800, there canbe less internal stress remaining in the developed master. A protectivelayer also may be provided on the negative photoresist layer, oppositethe substrate, as will be described below.

Additional discussion of the use of back-side imaging and/or negativephotoresist according to some embodiments of the present invention nowwill be provided. In particular, as was described above, it may bedifficult to create desired shapes for optical microstructures usingstandard lithographic approaches, particularly when applied to thickfilms of photoresist, i.e., layers of photoresist that are thicker thanabout 10 μm. Issues of uniformity of the thickness of the photoresistand quality of the photoresist surface can also interfere with theprocess. Given its base application in integrated circuit fabrication,photolithography has conventionally been performed on substrates such assilicon or other semiconductors which generally are not transparent tothe wavelengths of radiation used in the photolithographic process.Accordingly, front-side exposure is conventionally made from the air orfree side of the coating of photoresist, remote from the substrate.

In contrast, some embodiments of the present invention exposephotoresist through the substrate. Since some embodiments of the presentinvention need not be concerned with the electrical properties of thesubstrate that form the master, material such as plastics that aretransparent to the wavelengths of radiation that are being employed, maybe used. Thus, the photoresist can be exposed through the substrate.Although back-side exposure is applicable in principle to both positiveand negative photoresists, it may be particularly beneficial when usingnegative photoresist.

When exposed through the substrate, negative photoresist can naturallyform shapes with their bases adjacent the substrate. In contrast,front-side exposures generally involve some attenuation of the beamenergy as it penetrates through the photoresist film. This attenuationgenerally provides more exposure on the top of the photoresist than atthe base thereof, resulting in undercutting. With back-side exposure,there also may be attenuation, but the attenuation can be in the desireddirection, with the base of the structure receiving more exposure thanthe top.

Using back-side exposure, the height of the feature to be formed alsocan be rendered independent of the thickness of the photoresist. Thismay be difficult with front-side exposure, since the exposure may needto proceed all the way through the photoresist, from the outer surfaceof the photoresist to the base thereof, in order to not be washed away.Accordingly, some embodiments of the present invention can make shapesof varying heights, and the uniformity of the thickness of thephotoresist and the quality of the photoresist surface need not play acritical role in determining the quality of the optical microstructures.

FIG. 20 illustrates optical microstructures according to someembodiments of the present invention. As shown in FIG. 20, these opticalmicrostructures include a substrate 2010 and a patterned layer ofnegative photoresist 2020 on the substrate 2010, which is patterned todefine therein optical microstructures 2032. In some embodiments, thenegative photoresist 2020 is sensitive to radiation at an imagingfrequency, and the substrate 2010 is transparent to the imagingfrequency.

In some embodiments, the optical microstructures comprise a plurality ofoptical microstructures 2032 including bases 2034 adjacent the substrate2010 and tops 2036 remote from the substrate 2010 that are narrower thanthe bases 2034. In some embodiments, the substrate 2010 is a flexiblesubstrate. In other embodiments, the optical microstructures comprise aplurality of hemispherical sections including bases 2034 adjacent thesubstrate and tops 2036 remote from the substrate. In some embodiments,the substrate 2010 and the patterned layer of negative photoresist 2020provide an optical microstructure master 2000.

In some embodiments, the substrate 2010 is cylindrical, ellipsoidal orpolygonal in shape. In other embodiments, the substrate 2010 is at leastone foot long, one foot wide and/or one square foot in area. In yetother embodiments, the microstructures comprise microlenses. In stillother embodiments, the optical microstructures comprise at least aboutone million optical microstructures 2032. In still other embodiments,the photoresist 2020 may be a negative photoresist. Opticalmicrostructures of FIG. 20 may be fabricated according to any of themethods that were described above in connection with FIGS. 1-14 and/or17-19.

Embodiments of the present invention that can allow mass production ofoptical microstructure masters, which can be used to master largenumbers of optical microstructures, now will be described. Inparticular, FIG. 21 is a flowchart of operations that may be performedto fabricate optical microstructures. As shown in Block 2110, an opticalmicrostructure master that comprises a radiation sensitive layersandwiched between a pair of outer layers is imaged on an imagingplatform. Any of the imaging platforms and/or techniques that weredescribed in any of the previous figures may be used. Moreover, otherembodiments of imaging platforms and/or techniques will be describedbelow. In some embodiments the pair of outer layers comprises a firstouter layer adjacent the imaging platform and a second outer layerremote from the imaging platform. It will be understood that, as usedherein, the terms “first” and “second” are merely used to denote twodifferent outer layers, and that the positions and/or functions of thefirst and second outer layers may be reversed from those describedherein.

Then, referring to Block 2120, at least one of the outer layers isremoved. As will be described in detail below, in some embodiments, thefirst outer layer is removed from the radiation sensitive layer, tothereby separate the radiation sensitive layer and the second outerlayer from the imaging platform, while the first outer layer at leasttemporarily remains on the imaging platform. In other embodiments of thepresent invention, at least one outer layer is removed from the imagingplatform by removing the optical microstructure master, including theradiation sensitive layer sandwiched between the first and second outerlayers, from the imaging platform. Subsequent processing may beperformed to develop the imaged radiation sensitive layer and to createsecond generation stampers and third generation end products from thedeveloped radiation sensitive layer.

FIG. 22 is a flowchart of operations that may be performed to fabricateoptical microstructures according to other embodiments of the presentinvention. In particular, as shown in FIG. 22, at Block 2210, an opticalmicrostructure master blank or precursor is fabricated by sandwiching aradiation sensitive layer between a pair of outer layers. In someembodiments, a precursor or blank for an optical microstructure masterincludes a pair of closely spaced apart flexible webs and a radiationsensitive layer that is configured to accept an image of opticalmicrostructures, between the pair of closely spaced apart flexible webs,as will be described in detail below.

Still referring to FIG. 22, at Block 2220, the master blank is placed onan imaging platform. Many examples will be provided below. At Block2230, the master blank is imaged to define optical microstructures. AtBlock 2240, at least one outer layer is removed, for example as wasdescribed in connection with Block 2120 of FIG. 21. Many other exampleswill be provided below. At Block 2250, a second generation stamper iscreated by contacting the optical microstructures in the radiationsensitive layer to a stamper blank. Then, at Block 2260, end products,such as microlenses for computer displays or televisions, are created bycontacting the stamper to final product blanks.

FIG. 23 is a schematic diagram of systems and methods that may be usedto fabricate optical microstructure master blanks according to someembodiments of the present invention, which may correspond to Block 2210of FIG. 22. As shown in FIG. 23, a first roller 2340 a or otherconventional supply source contains thereon a flexible web of a firstouter layer 2310. A radiation sensitive layer coating station 2350 isconfigured to coat a radiation sensitive layer 2320 on the first outerlayer 2310 using one or more conventional coating techniques. As wasdescribed above, for example in connection with FIG. 18, someembodiments of the present invention can allow optical microstructuremasters to be imaged in the radiation sensitive layer 2320 independentof thickness variations of the radiation sensitive layer 2320.

Still referring to FIG. 23, a second roller 2340 b or other conventionalsupply source contains thereon a web of a second outer layer 2330. Alamination station, which can include a roller 2340 c and/or otherconventional laminating devices, is used to laminate the second outerlayer 2330 to the radiation sensitive layer 2320 opposite the firstouter layer 2310, which is then gathered on a take-up roller 2340 d orother storage device. Thus, as shown in FIG. 24, a blank or precursorstructure 2400 for an optical microstructure master, according to someembodiments of the invention, includes a pair of closely spaced apartflexible webs 2310 and 2330, and a radiation sensitive layer 2320 thatis configured to accept an image of optical microstructures, between thepair of closely spaced apart flexible webs 2310 and 2330.

Optical microstructure master precursors 2400 of FIG. 24 may be used inany of the embodiments described above in connection with FIGS. 1-22. Insome embodiments, the radiation sensitive layer 2320 can embody thelayers 110, 810, 810′, 810′″, 1210, 1310, 1610 and/or 2020 that weredescribed above. In some embodiments, the second outer layer 2330 canprovide a flexible, optically transparent substrate, which maycorrespond to the substrate 800, 800′, 800″, 1200, 1600 and/or 2010 thatwere described above. The first outer layer 2310 can provide a releaselayer that may be placed adjacent an imaging platform in any of thepreceding figures, to allow release of the optical microstructure masterprecursor 2400 from an imaging platform after imaging. The first outerlayer 2310 may also function as a pellicle, which can protect theradiation sensitive layer 2320 from contaminants prior to, during and/orafter imaging, so that fabrication, storage and/or imaging of theoptical microstructure master precursors 2400 need not take place in aclean room environment. The first outer layer 2310 also may function asan optically absorbing, reflective or transmissive layer during theimaging process. Combinations of these and/or other properties also maybe provided in the first outer layer 2310. It also will be understoodthat the first outer layer 2310 and/or the second outer layer 2330 cancomprise a plurality of sublayers.

Still referring to FIG. 24, in some embodiments of the presentinvention, the radiation sensitive layer 2320 is a negative photoresistlayer, as was described extensively above. In other embodiments of thepresent invention, the first outer layer 2310 and the second outer layer2330 are identical. In still other embodiments, the negative photoresistlayer 2320 is sensitive to radiation at a predetermined frequency, andthe second outer layer 2330 is transparent to radiation at thepredetermined frequency. In still other embodiments of the presentinvention, the second outer layer 2330 is transparent to radiation atthe predetermined frequency and the first outer layer 2310 is opaque toradiation at the predetermined frequency. As was also already described,the structure and/or functions of the first and second outer layers maybe reversed.

In some embodiments of the present invention, the optical microstructuremaster blank or precursor 2400 includes a second outer layer 2330 thatis transparent to the wavelengths of radiation used in exposure, isflat, relatively free of imperfections (i.e., of optical quality), clearand without haze. It may be desirable for the radiation sensitive layer2320 to adhere well to the second outer layer 2330, and it may bedesirable for the second outer layer 2330 to be relatively impervious tothe chemicals and thermal processes that may be involved in developingthe radiation sensitive layer. In some embodiments, the second outerlayer 2330 comprises plastic, such as polyester, polycarbonate and/orpolyethylene. The first outer layer 2310 also may comprise plastic, suchas polyester, polycarbonate and/or polyethylene.

Embodiments of the present invention as shown in FIGS. 23 and 24 may becontrasted with conventional mastering approaches for opticalmicrostructures, which generally have been performed on expensive and/orinflexible substrates such as glass, silica or silicon. These mastersmay not exceed 300 mm in diameter. In contrast, embodiments of thepresent invention as shown in FIGS. 23 and 24 can fabricate large areamaster blanks from webs, which may be more than about a foot wide insome embodiments. The master blanks can be set up for exposure, and canpermit rapid turnaround of the imaging platform or mastering machine.Thus, embodiments of the present invention as shown in FIGS. 23 and 24can be used where the imaging platforms may be expensive and/or requirelong lead time items. The master blanks can be placed on the imagingplatform for imaging, and then taken off the imaging platform to freethe imaging platform for another master blank, as will be described indetail below.

FIGS. 25A-25E are cross-sectional views of systems and methods offabricating optical microstructures according to some embodiments of thepresent invention. As shown in FIG. 25A, a flexible opticalmicrostructure master blank or precursor 2400 of FIG. 24 is wrappedaround a cylindrical imaging platform 2500, which may correspond to oneof the imaging platforms of FIGS. 1-4, 7 and/or 9 that were describedabove. In some embodiments, imagine can take place through the secondouter layer 2330 according to any of the techniques for back-sideimaging that were described above, to produce an image of opticalmicrostructures in the radiation sensitive layer 2320. Accordingly, FIG.25A illustrates some embodiments of Blocks 2110, 2220 and/or 2230.

Then, referring to FIG. 25B, in some embodiments, the first outer layer2310 can act as a release layer, which can permit removal of the secondouter layer 2330 and the imaged radiation sensitive layer 2320′ from thefirst outer layer 2310. The imaged radiation sensitive layer 2320′ isdeveloped to produce optical microstructures 2320″ as shown in FIG. 25C.Thus, FIG. 25C illustrates another embodiment of a completed opticalmicrostructure master 2550, and FIGS. 25B and 25C illustrate embodimentsof Blocks 2120 and/or 2240.

A second generation of optical microstructures, also referred to as astamper, is created from the master 2550 that contains the opticalmicrostructures 2320″ in the developed radiation sensitive layer, bycontacting the optical microstructures 2320″ to a stamper blank. Thismay correspond to Block 2250. In particular, as shown in FIG. 25D,contacting to a stamper blank may take place by mounting the master 2550on a planar stamping platform 2510, and pressing the planar stampingplatform 2510 against a stamper blank 2520 in the direction shown byarrow 2512. In other embodiments, as shown in FIG. 25E, the master 2550is placed on a cylindrical stamping platform 2540, and rolled in thedirection of arrow 2542 against a stamper blank 2520, to create astamper.

FIGS. 26A and 26B illustrate other embodiments of the present invention,which may be formed in operations of Blocks 2120 and/or 2240. In FIG.26A, the step of removing at least one outer layer is performed byremoving the entire imaged master blank 2400 from the imaging platform2500. Then, in FIG. 26B, the first outer layer 2310 is removed from theimaged radiation sensitive layer 2320′, and the imaged radiationsensitive layer 2320′ is developed, to provide the master 2550.

FIG. 27 illustrates yet other embodiments that may be formed inoperations of Blocks 2110, 2220 and/or 2230, according to otherembodiments of the present invention, wherein the optical microstructuremaster precursor 2400 is imaged on a planar imaging platform 2700, whichmay correspond to the imaging platform 1000 or 1100 of respective FIG.10 or 11. After imaging of FIG. 27, removal (Blocks 2120 and/or 2240)may take place as was described in connection with FIG. 25B and/or FIG.26A. Moreover, stamping operations may take place as was described inconnection with FIGS. 25D and/or 25E. Accordingly, imaging may takeplace on a planar or nonplanar imaging platform, and stamping may takeplace on a planar or nonplanar stamping platform, which may or may notbe the same platform as the imaging platform, according to variousembodiments of the present invention.

Additional discussion of FIGS. 21-27, according to some embodiments ofthe present invention, now will be provided. In particular, an opticalmicrostructure master blank or precursor 2400 may be held on acylindrical imaging platform, such as platform 2500 of FIG. 25A, or on aplanar imaging platform, such as platform 2700 of FIG. 27, usingelectrostatic charge, vacuum chuck, adhesive tape and/or otherconventional techniques which may be depend on the thickness, weightand/or flexibility of the master blank 2400. Moreover, after imaging orexposure in FIGS. 25A and/or 27, the optical microstructure masterprecursor 2400 undergoes post-exposure development of the radiationsensitive layer, to create a master, such as the master 2550 of FIGS.25C and/or 26B.

It will be understood by those having skill in the art that removableoptical microstructure master precursors 2400 can be used for bothfront-side and back-side exposures, and with both positive and negativephotoresists. However, some embodiments of the present invention useback-side exposure and negative photoresist, as was describedextensively above. When using back-side exposure and negativephotoresist, the first outer layer 2310 may be removed after imaging.Removal of the first outer layer 2310 may take place on the imagingplatform as was described, for example, in FIGS. 25A and 25B, or afterremoval of the imaged master from the imaging platform as was describedin FIGS. 26A and 26B.

Accordingly, embodiments of the present invention that were describedabove in connection with FIGS. 21-27 can provide for removing of thefirst outer layer 2310 from the imaged radiation sensitive layer 2320′,to thereby remove the imaged radiation sensitive layer 2320′ from theimaging platform 2500 or 2700 after imaging has taken place. A stampermay be created from the optical microstructures 2320″ by contacting theoptical microstructures 2320″ to a stamper blank 2520. In otherembodiments, the first outer layer 2310 is separated from the imagingplatform 2500 or 2700 after imaging has taken place. Then, the firstouter layer 2310 is separated from the imaged radiation sensitive layer2320′. A stamper may be created from the optical microstructures 2320″by contacting the optical microstructures 2320″ to a stamper blank 2520.In some embodiments, the optical microstructures are pressed against astamper blank (FIG. 25D). In other embodiments, the opticalmicrostructures are rolled against a stamper blank (FIG. 25E).

Removable optical microstructure master blanks as were described inconnection with FIGS. 21-27 may be particularly suitable for massproduction of masters and stampers according to some embodiments of thepresent invention. In particular, as shown in FIG. 28, imaging of anoptical microstructure master precursor 2400 may take place, whilecreating stampers from an optical microstructure master 2550 that waspreviously imaged. Thus, imaging of an optical microstructure masterprecursor and creating stampers from a previously imaged microstructuremaster precursor at least partially overlap in time.

Thus, a potentially expensive and/or long lead time optical imagingplatform 2500 may be used on an almost continuous basis for imaging, byremoving an optical microstructure master precursor from the imagingplatform 2500, after imaging. However, in other embodiments of thepresent invention, the imaging platform also may be used as a stampingplatform, by not removing the imaged optical microstructure masterprecursor from the imaging platform. It will be understood that in FIG.28, cylindrical and/or planar imaging platforms may be used, andpressing and/or rolling of the master against the stamper blank may beused, as was described in connection with FIGS. 25-27.

Mastering on removable substrates can permit the same machine and/orplatform to be used to form masters with a number of different radiationsensitive layers, coated on different substrates of varying thickness.The use of negative photoresist and exposure through the substrate canpermit use of removable masters according to some embodiments of thepresent invention, since the surface of the photoresist that is attachedto the imaging platform can be removed during developing and, thus, neednot be involved in the final production of the optical elements.Similarly, it is possible to employ simple, rapid and/or relativelyinexpensive techniques of coating photoresist onto the substrate whenusing negative photoresists and back-side exposure, according to someembodiments of the present invention.

Accordingly, some embodiments of the present invention can provide amaster for replicating large numbers of optical microstructures that areformed by multiple exposures through a transparent, removable substrate,into negative photoresist on a removable substrate. This can providecommercially viable mastering systems, methods and products for largenumbers of optical microstructures. In some embodiments of the presentinvention, masters of at least about one foot long, about one foot wideand/or about one foot square, containing up to about one million or moremicrostructures of about 100 μm or smaller in size, can be mastered inabout 8 to 15 hours. Optical elements with arbitrary shapes can beformed by varying exposure from point to point in the master. Thespacing of the elements in the master can be varied from widelyseparated to overlapping. The master can be created on a removablesubstrate, so that the mastering platform can be reconfigured forfurther mastering work.

Finally, it will be understood that embodiments of the present inventionhave been described herein relative to the fabrication of opticalmicrostructures, which may include microlenses, optical gratings,microreflectors and/or other optically-absorbing transmissive and/orreflective structures, the individual sizes of which are on the order ofmicrons, for example on the order of about 5 μm to about 1000 μm, insize. However, it will be understood that other embodiments of thepresent invention may be used to fabricate mechanical microstructuressuch as pneumatic, hydraulic and/or microelectromechanical system (MEMS)microstructures, which may be used for micro-fluidics, micro-pneumaticsand/or micromechanical systems, the individual sizes of which are on theorder of microns, for example on the order of about 5 Ξm to about 1000μm, in size.

In the drawings and specification, there have been disclosed embodimentsof the invention and, although specific terms are employed, they areused in a generic and descriptive sense only and not for purposes oflimitation, the scope of the invention being set forth in the followingclaims.

1. A method of fabricating optical microstructures comprising: rotatinga cylindrical platform that includes a radiation sensitive layer thereonabout an axis thereof; while simultaneously axially rastering aradiation beam across a portion of the radiation sensitive layer; andwhile simultaneously continuously translating the cylindrical platformand/or radiation beam axially relative to one another, whereinsimultaneously axially rastering comprises: simultaneously axiallyrastering a radiation beam along first and second opposite axialdirections across a portion of the radiation sensitive layer to imagethe optical microstructures in the radiation sensitive layer along thefirst axial direction and to blank the radiation beam along the secondaxial direction.
 2. A method according to claim 1 wherein simultaneouslyaxially rastering comprises simultaneously axially rastering a radiationbeam across a portion of the radiation sensitive layer while varyingamplitude of the radiation beam.
 3. A method according to claim 1wherein simultaneously axially rastering comprises simultaneouslyaxially rastering a radiation beam across at least a portion of theradiation sensitive layer while continuously varying amplitude of theradiation beam.
 4. A method according to claim 1 wherein simultaneouslyaxially rastering a radiation beam comprises simultaneously axiallyrastering a laser beam.
 5. A method according to claim 4 whereinsimultaneously axially rastering a laser beam comprises: generating acontinuous wave laser beam; modulating the laser beam to vary anamplitude thereof; and oscillating the laser beam to raster the laserbeam across a portion of the radiation sensitive layer.
 6. A methodaccording to claim 1 wherein simultaneously axially rastering isperformed at sufficient speed, relative to rotating, such that theradiation beam images an optical microstructure over a plurality ofscans of the radiation beam.
 7. A method according to claim 1 furthercomprising: simultaneously varying a focal length of the radiation beamto at least partially compensate for radial variation in the cylindricalplatform and/or thickness variation in the radiation sensitive layer. 8.A method according to claim 1 further comprising: simultaneously varyinga focal length of the radiation beam to image portions of the opticalmicrostructures at varying depths in the radiation sensitive layer.
 9. Amethod according to claim 1 wherein the cylindrical platform is at leastabout one foot in circumference and/or at least about one foot in axiallength.
 10. A method of fabricating optical microstructures comprising:rotating a cylindrical platform that includes a radiation sensitivelayer thereon about an axis thereof; while simultaneously axiallyrastering a radiation beam across a portion of the radiation sensitivelayer; and while simultaneously continuously translating the cylindricalplatform and/or radiation beam axially relative to one another; whereinthe cylindrical platform is at least about one foot in circumferenceand/or at least about one foot in axial length; and wherein rotating isperformed at angular velocity of at least about 1 revolution per minute.11. A method according to claim 10 wherein simultaneously axiallyrastering is performed at frequency of at least about 1 kHz.
 12. Amethod of fabricating optical microstructures comprising: rotating acylindrical platform that includes a radiation sensitive layer thereonabout an axis thereof; while simultaneously axially rastering aradiation beam across a portion of the radiation sensitive layer; andwhile simultaneously continuously translating the cylindrical platformand/or radiation beam axially relative to one another; wherein rotatingand simultaneously axially rastering are performed continuously for atleast about 1 hour.
 13. A method according to claim 12 wherein rotatingand simultaneously axially rastering are performed continuously for atleast about 1 hour to fabricate at least about one million opticalmicrostructures.
 14. A method of fabricating optical microstructurescomprising: rotating a cylindrical platform that includes a radiationsensitive layer thereon about an axis thereof; while simultaneouslyaxially rastering a radiation beam across a portion of the radiationsensitive layer; and while simultaneously continuously translating thecylindrical platform and/or radiation beam axially relative to oneanother; wherein the optical microstructures comprise microlenses.
 15. Amethod according to claim 1 further comprising: developing the opticalmicrostructures that are imaged in the radiation sensitive layer toprovide an optical microstructure master.
 16. A method of fabricatingoptical microstructures comprising: rotating a cylindrical platform thatincludes a radiation sensitive layer thereon about an axis thereof;while simultaneously axially rastering a radiation beam across a portionof the radiation sensitive layer; and while simultaneously continuouslytranslating the cylindrical platform and/or radiation beam axiallyrelative to one another; wherein the cylindrical platform also includesa substrate on the radiation sensitive layer that is transparent to theradiation beam and wherein simultaneously axially rastering comprisessimultaneously axially rastering a radiation beam through the substratethat is transparent thereto across a portion of the radiation sensitivelayer.
 17. A method according to claim 16 wherein the radiationsensitive layer is a negative photoresist layer such that portions ofthe negative photoresist layer that are exposed to the radiation beamremain after development.
 18. A method according to claim 1 wherein theradiation sensitive layer is a negative photoresist layer such thatportions of the negative photoresist layer that are exposed to theradiation beam remain after development.
 19. A method according to claim16 wherein the substrate is a flexible substrate.
 20. A method accordingto claim 1 wherein rotating comprises: rotating a cylindrical platformthat includes thereon a radiation sensitive layer sandwiched between apair of outer layers about an axis thereof.
 21. A method according toclaim 20 wherein simultaneously axially rastering is followed by:removing at least one of the outer layers.
 22. A method according toclaim 20 wherein the pair of outer layers comprises a first outer layeradjacent the cylindrical platform and a second outer layer remote fromthe cylindrical platform that is transparent to the radiation beam, andwherein simultaneously axially rastering comprises simultaneouslyaxially rastering the radiation beam through the second outer layeracross at least a portion of the radiation sensitive layer.
 23. A methodaccording to claim 22 wherein the radiation sensitive layer is anegative photoresist layer.
 24. A method according to claim 21 whereinthe removing comprises: separating the first outer layer from thecylindrical platform; and separating the first outer layer from theradiation sensitive layer.
 25. A method of fabricating opticalmicrostructures comprising: rotating a cylindrical platform thatincludes a radiation sensitive layer thereon about an axis thereof;while simultaneously axially rastering a laser beam across a portion ofthe radiation sensitive layer while continuously varying amplitude ofthe laser beam; and while simultaneously translating the cylindricalplatform and/or laser beam axially relative to one another; whereinsimultaneously axially rastering is performed at sufficient speed,relative to rotating, such that the laser beam images an opticalmicrostructure over a plurality of scans of the laser beam.
 26. A methodaccording to claim 25 further comprising: simultaneously varying a focallength of the laser beam.
 27. A method according to claim 26 whereinsimultaneously axially rastering comprises: simultaneously axiallyrastering a laser beam along first and second opposite axial directionsacross a portion of the radiation sensitive layer to image the opticalmicrostructures in the radiation sensitive layer along the first axialdirection and to blank the laser beam along the second axial direction.28. A method according to claim 27 wherein the cylindrical platform isat least about one foot in circumference and/or at least about one footin axial length.
 29. A method according to claim 28 wherein rotating andsimultaneously axially rastering are performed continuously for at leastabout 1 hour to fabricate at least about one million opticalmicrostructures.
 30. A method according to claim 29 wherein the opticalmicrostructures comprise microlenses.
 31. A method according to claim 30further comprising: developing the microlenses that are imaged in theradiation sensitive layer to provide a microlens master.
 32. A method offabricating optical microstructures comprising: rotating a cylindricalplatform that includes a radiation sensitive layer thereon about an axisthereof; while simultaneously axially rastering a laser beam across aportion of the radiation sensitive layer while continuously varyingamplitude of the laser beam; and while simultaneously translating thecylindrical platform and/or laser beam axially relative to one another;wherein the radiation sensitive layer is a negative photoresist layersuch that portions of the negative photoresist layer that are exposed tothe radiation beam remain after development; and wherein the cylindricalplatform also includes a substrate on the negative photoresist layerthat is transparent to the laser beam and wherein simultaneously axiallyrastering comprises simultaneously axially rastering a laser beamthrough the substrate that is transparent thereto across a portion ofthe negative photoresist layer.
 33. A method according to claim 32wherein the cylindrical platform also includes a release layer betweenthe negative photoresist layer and the cylindrical platform.